I'm not an expert on this topic and while I have spent some time in the US, my experience is limited. The particular case of two highways intersecting is one t

I'm not an expert on this topic and while I have spent some time in the US, my experience is limited. The particular case of two highways intersecting is one thing. Go ahead and have your diverging diamond interchange there. However, I don't believe Interstate-Interstate-Crossings are the most common use in the US? See for example https://wsdot.wa.gov/travel/traffic-safety-methods/diverging-diamond-interchange https://wsdot.wa.gov/travel/traffic-safety-methods/diverging.... Three crossings, none are between two interstates? Or am I misreading this? I actually believe it comes down to this: You only need the diverging diamond interchange if you build a highway in tight spaces, such as inside cities. In particular you want them on heavily frequented entries/exits that would otherwise let traffic back up into the cities. Thus, the interchange is at or close to a location with a lot of important destinations, otherwise you wouldn't build it there. Not having that interchange then open to traffic other than cars then clearly makes it harder to cross the highway at these places. You'll have to go up or down each of the roads until you hit an over- or underpass or crossing. In my experience, in the US, this is generally very far - as of course everything is already bigger than in other places because of parking lots.